RFID tag and manufacturing method thereof

ABSTRACT

An RFID tag having a tag antenna and an LSI chip, comprising: a power-supply pattern on which the LSI chip is mounted; a patch antenna that functions as the tag antenna; and a high-frequency connection section that makes a high-frequency connection between the power-supply pattern and the patch antenna. The high-frequency connection section is formed, for example, by forming a slot in the patch antenna, layering one end of a small dipole antenna that functions as the power-supply pattern over the slot so that it crosses over the slot, and supplying power from the small dipole antenna to the patch antenna.

BACKGROUND OF THE INVENTION

The present invention relates to an RFID tag and manufacturing methodthereof, and more particularly an RFID tag that comprises a patchantenna (flat antenna) as the tag antenna, and which is capable ofdemonstrating the required characteristics even when applied to anobject such as a electrically conductive body, electricallynon-conductive body or a body including liquid, and to the manufacturingmethod thereof.

Conventionally, in the distribution industry, transport industry and thelike, a method of printing or sticking barcodes on a product itself oron the product packaging, and then reading that barcode with a barcodereader has been widely used as a method for managing individual productinformation. However, in that barcode processing method, when readingthe barcode, the barcode reader must come in contact with the barcode,which makes the work of reading troublesome. Moreover, in theconventional barcode processing method, there is a problem in that it isnot possible to add new information or update the information of thebarcode itself.

Therefore, recently, a method of attaching an RFID (Radio FrequencyIdentification) tag to products in the place of a barcode, and readingthat product information without contact using radio waves(electromagnetic coupling) is needed and is in the progress of being putinto practical use. An RFID tag is a tag that has an IC card function towhich a radio communication function for information has been added, andhas a non-volatile memory that is capable of storing information, butdoes not have a battery (power source). Therefore, when readinginformation from the RFID tag memory without contact, a tag reader isconstructed so that it supplies power to the RFID tag usingelectromagnetic waves, and reads information from the tag memory. Withthis kind of RFID tag, it is possible to greatly improve workability,and by using a technology such as a verification function or encodingbetween the reader and RFID tag, it is possible to ensure good security.

FIG. 38 is a drawing explaining an RFID tag, where a reader 1 transmitsa radio signal (electromagnetic wave) of modulated data from an antenna2 to an RFID tag 3. The antenna 3 a of the RFID tag 3 inputs thereceived signal to a rectifier circuit 3 b and a modulation anddemodulation circuit 3 c. The rectifier circuit 3 b converts the radiosignal to DC voltage, and supplies this DC voltage to the modulation anddemodulation circuit 3 c and a logic circuit 3 d, and that voltagefunctions as a power supply. The modulation and demodulation circuit 3 cdemodulates control data that was sent from the reader 1, and inputs theresult to the logic circuit 3 d. The logic circuit 3 d performs logicprocessing according to the control data (command), for example, readsinformation that is stored in an internal memory and inputs thatinformation to the modulation and demodulation circuit 3 c. Themodulation and demodulation circuit 3 c uses the information that wasinput from the logic circuit 3 d to modulate a carrier signal, andtransmits that signal as a radio signal from the antenna 3 a to thereader 1.

Various types of RFID tags have been proposed. One of those is an RFIDtag that is constructed by mounting an antenna pattern for radiocommunication and an IC chip (LSI) on a dielectric base sheet made ofplastic, paper or the like. When this kind of RFID tag is attached to anelectrically non-conductive object, the desired performance, such ascommunication distance and the like, is obtained. However, when thiskind of RFID tag is attached to metal such as steel, the metal obstructsthe radio waves used for communication with the RFID tag, and problemsoccur such as a decrease in the communication distance.

FIG. 39 is a drawing explaining the occurrence of this kind of problem,where (A) of FIG. 39 shows the case in which an RFID tag having ahalf-wave length dipole antenna pattern is attached to an electricallynon-conductive object (not shown in the figure), and the power(open-circuit V) necessary for the IC chip is generated in the dipoleantenna DP by the radio waves emitted from the reader/writer antenna.Also, current I flows in the dipole antenna making it possible totransmit an electromagnetic signal to the reader/writer antenna.

However, when an RFID tag having a dipole antenna pattern is attached toa metal object, the tangential component of the electric field on themetal surface becomes ‘0’ from the boundary condition, and thesurrounding electric field becomes ‘0’. Therefore, it is not possible tosupply the necessary power to the IC chip of the RFID tag. Also, it isnot possible to transmit (scatter) an electromagnetic wave to thereader/writer antenna from the tag antenna. In other words, as shown in(B) of FIG. 39, in the case of an RFID tag having a dipole antennapattern DP that is attached to a metal object MTL, when current I flowsin the dipole antenna DP, an image IMG, in which current flows in theopposite direction, is generated in the metal object MTL according tothe mapping principle. This image cancels out the electric field that isgenerated by the dipole antenna current I, and thus it is not possibleto supply the necessary power to the IC chip of the RFID tag, and itbecomes impossible to transmit an electromagnetic wave to thereader/writer antenna from the tag antenna. Due to the aforementionedproblems, an RFID tag having a tag antenna capable of transmitting andreceiving electromagnetic waves without degradation of the antenna gaineven when attached to a metal surface is desired.

As shown in (C) of FIG. 39, reducing the image effect by increasing thedistance D from the surface of the metal object MTL to the dipolepattern DP is feasible, however, there is a problem in that thethickness of the RFID tag increases. Also, an RFID system in the UHFband has the advantage of having a long communication distance comparedwith other frequency bands, however, the length of a dipole type tagantenna for the UHF band normally must be a half wave length(approximately 16 cm). This length can be ensured and made more compactby attaching and bending the tag antenna around a dielectric body,however, the bandwidth becomes narrow. Taking the aforementioned probleminto consideration, desired is an RFID tag that is small and compact andthat has an antenna being capable of large bandwidth without degradationof the antenna gain even when the RFID tag is made small and compact.

Also, in order to efficiently supply the receiving power of the tagantenna to the LSI chip, the impedances of the tag antenna and the LSIchip must be matched (impedance matching). In order to accomplish this,an impedance conversion circuit is necessary, however, that wouldincrease the manufacturing cost of the RFID tag. Therefore, it isnecessary to perform impedance matching of the tag LSI and tag antennawithout using an impedance conversion circuit. In other words, desiredis an RFID tag that has an antenna for which impedance matching with theLSI chip is possible without having to use an impedance conversioncircuit.

Conventional RFID tags having a dipole antenna have a problem in thatthe communication distance becomes poor when the RFID tag is attached tometal as described above. Therefore, some tag antennas have beendeveloped that are compatible with metal even in the UHF band (refer toJP2002-298106A), however all of these are large having a thickness of 4mm or more and length of 10 cm or more.

Therefore, the inventors of the present invention proposed an RFID taghaving a small antenna that is capable of transmitting and receivingelectromagnetic waves even when attached to a metal surface (refer toJP2006-53833A). As shown in FIG. 40, this proposed RFID tag 10comprises: a rectangular shaped dielectric member 11; atransmission/reception antenna pattern 12 that forms a loop antennaaround the surface of the dielectric member 11; and an IC chip 15 thatis electrically connected to the antenna pattern 12 by way of achip-mounting pad 13. With the RFID tag having this kind of loop antennaconstruction, transmission and reception of electromagnetic waves ispossible, it is possible to lengthen the communication length eventhough the RFID tag is thin and is attached to a metal, the gain isnearly constant over a wide band, and furthermore, impedance matching ispossible even without an impedance conversion circuit. However,manufacturing an RFID tag having loop antenna construction requirescomplicated processes such as side surface plating, or processing forwrapping an insulating film around the dielectric member, so there areproblems in that the manufacturing cost increases, or high precision isrequired for positioning the wrapping.

Therefore, recently, use of a patch antenna as an RFID antenna has beenproposed. With an RFID tag having this patch antenna construction, thereis no need for special work such as side-surface plating or wrapping asin the case of a RFID tag having loop antenna construction.

However, in order to use a patch antenna as an RFID tag antenna,impedance matching with the LSI chip of the RFID tag must be performed.Normally, supplying power to a patch antenna can be done such that poweris supplied to the patch antenna from a position that is matched to a50Ω power supply line, however the impedance of the LSI chip becomes adifferent value greater than 50Ω, so an impedance conversion circuit isnecessary. Also, with a conventional patch antenna it is necessary tomake holes in the patch antenna in order to supply power, so there is aproblem in that processing cost increases.

An RFID tag patch antenna has been proposed that does not need animpedance conversion circuit, and does not require making holes in theantenna in order to supply power (refer to U.S. Pat. No. 6,215,401).This proposed method is a method that supplies power to the patchantenna in a state in which the tag LSI is DC-connected to this patchantenna, and performs impedance matching by regulating the width andlength of the line used for connection, however, it has a problem inthat it is easy for construction of the power supply unit to becomecomplicated. Also, in the case of using a board having a low frequencyand low dielectric constant, the percentage of space occupied by theimpedance matching circuit pattern and quarter wavelength converter withrespect to the overall antenna becomes large.

SUMMARY OF THE INVENTION

Taking the above into consideration, the object of the present inventionis to provide an RFID tag and manufacturing method thereof for which thecommunication distance does not become poor even when attached to ametal and an object including liquid.

Another object of the present invention is to provide a RFID tag andmanufacturing method thereof for which it is not necessary to DC-makeholes in a patch antenna for power supply, and does not require aconnection to the patch antenna.

Moreover, another object of the present invention is to provide an RFIDtag and manufacturing method thereof for which an impedance conversioncircuit is not necessary.

Furthermore, another object of the present invention is to provide anRFID tag and manufacturing method thereof that is small and thin and hashigh gain.

RFID Tag

This invention is an RFID tag having a tag antenna and an LSI chip,comprising: a power-supply pattern on which the LSI chip is mounted; apatch antenna that functions as the tag antenna; and a high-frequencyconnection section that high-frequency connects the power-supply patternwith the patch antenna.

The RFID tag of the present invention, further comprises: a dielectricmember having the power-supply pattern, patch antenna and high-frequencyconnection section formed on one side, and a conductive pattern thatfunctions as ground formed on the other side; and a short-circuit unitthat forms a short circuit between one edge of the patch antenna andground along the side surface of the dielectric member.

In the RFID tag of this invention, a typical power-supply pattern is adipole antenna, monopole antenna or loop antenna.

In the RFID tag of this invention described above, a slot is formed inthe patch antenna (first path antenna), and one end of a small dipoleantenna that functions as a power-supply pattern is layered over theslot so that it crosses over the slot, and power is supplied from thesmall dipole antenna to the patch antenna.

In the RFID tag of this invention described above, a cutout section isformed in the patch antenna, one end of a small dipole antenna thatfunctions as a linear antenna is high-frequency connected with thecutout section, and power is supplied from the small dipole antenna tothe patch antenna.

In the RFID tag of this invention described above, the LSI chip ismounted in the center of the small dipole antenna, and another patchantenna (second patch antenna) is placed so that it has left-rightsymmetry with the first patch antenna with the LSI chip being in thecenter; and the positional relationship between the first patch antennaand one end of the small dipole antenna, and the positional relationshipbetween the second patch antenna and other end of the dipole antenna arethe same.

Manufacturing Method for an RFID Tag

This invention is a manufacturing method for an RFID tag having a tagantenna and an LSI chip, comprising steps of: forming a power-supplypattern on which an LSI chip is mounted, and a patch antenna thatfunctions as a tag antenna on the surface of a double-sided print boardby etching, so that the power-supply pattern and tag antenna arehigh-frequency connected; making a conductive pattern on the rearsurface of the print board ground; and mounting the LSI chip on thepower-supply pattern to create the RFID tag.

This invention comprises: a power-supply pattern on which the LSI chipis mounted; a patch antenna that functions as the tag antenna; and ahigh-frequency connection section that high-frequency connects thepower-supply pattern with the patch antenna, and since power is suppliedin high-frequency from the power-supply pattern to the patch antenna,there is no need to makes holes in the patch antenna, making it possibleto simplify the processing of the RFID tag and lower the processingcost.

Also, this invention uses a patch antenna as the tag antenna, so it isnot affected by the material properties of the ground side, therefore,the communication distance does not become poor even when the antenna isattached to a metal or an object including liquid.

Moreover, with this invention, the gain of the patch antenna is greaterthan a loop antenna or the like, and by adjusting the thickness,conductivity of the metal, dielectric loss or the like, it is possibleto make the gain of the patch antenna even greater, and to make the sizesmaller.

Furthermore, with this invention, by connecting a loop pattern thatfunctions as a parallel inductor to the dipole antenna or monopoleantenna that functions as a power-supply pattern, and adjusting thedimensions of that pattern or adjusting the length of the power-supplypattern, the slot length, cutout length or the like, it is possible tomatch impedance with the LSI chip, and thus an impedance conversioncircuit is not necessary.

Other features and advantages of the present invention will be apparentfrom the following description taken in conjunction with theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a drawing explaining the RFID tag of a first embodiment of thepresent invention.

FIG. 2 is a drawing explaining the radio waves that are emitted from apatch antenna.

FIG. 3 is a top view of the RFID tag of a second embodiment of thepresent invention.

FIG. 4 is a drawing showing the actual dimensions and boardcharacteristics of the RFID of the second embodiment.

FIG. 5 shows various simulation results as the frequency changes from850 MHz to 980 MHz.

FIG. 6 is a Smith chart showing the impedance of a tag antenna.

FIG. 7 is a drawing of an equivalent circuit of an RFID tag thatcomprises an LSI chip and tag antenna.

FIG. 8 is a drawing showing the gain characteristics of a tag antenna asthe frequency changes from 850 MHz to 980 MHz.

FIG. 9 is a drawing showing the S parameter (S11) characteristics as thefrequency changes from 850 MHz to 980 MHz.

FIG. 10 is a drawing showing the communication distance characteristicsas the frequency changes from 850 MHz to 980 MHz.

FIG. 11 is a drawing explaining the impedance plot when the parallelinductor dimension s2 is adjusted, and the frequency on the Smith chartis changed.

FIG. 12 is a top view of the RFID tag of a third embodiment of theinvention.

FIG. 13 is a top view of the case in which tag antennas of the firstembodiment are connected in parallel.

FIG. 14 is a top view of the RFID tag of a fourth embodiment of thepresent invention.

FIG. 15 is a drawing showing the actual dimensions and boardcharacteristics of the RFID tag of the fourth embodiment.

FIG. 16 shows various simulation results for the fourth embodiment asthe frequency changes from 850 MHz to 980 MHz.

FIG. 17 is a Smith chart showing the impedance of a tag antenna.

FIG. 18 is a drawing showing the gain characteristics of a tag antennaas the frequency changes from 850 MHz to 980 MHz.

FIG. 19 is a drawing showing the S parameter (S11) characteristics asthe frequency changes from 850 MHz to 980 MHz.

FIG. 20 is a drawing showing the communication distance characteristicsas the frequency changes from 850 MHz to 980 MHz.

FIG. 21 is a drawing explaining the impedance plot when the parallelinductor dimension s2 is adjusted, and the frequency on the Smith chartis changed.

FIG. 22 is a top view of the RFID tag of a fifth embodiment.

FIG. 23 is a drawing showing the actual dimensions and boardcharacteristics of the RFID tag of the fifth embodiment.

FIG. 24 is a Smith chart showing the impedance of a tag antenna.

FIG. 25 is a drawing showing the gain characteristics of a tag antennaas the frequency changes from 840 MHz to 980 MHz.

FIG. 26 is a drawing showing the S parameter (S11) characteristics asthe frequency changes from 840 MHz to 980 MHz.

FIG. 27 is a drawing showing the communication distance characteristicsas the frequency changes from 840 MHz to 980 MHz.

FIG. 28 is a drawing explaining a sixth embodiment of the invention.

FIG. 29 is a drawing explaining the electric field in the Y-axisdirection of the patch antenna.

FIG. 30 is a drawing showing the impedance/frequency characteristicplotted on a Smith chart for the impedance of the sixth embodiment.

FIG. 31 is a drawing showing the frequency characteristic of thecommunication distance.

FIG. 32 is a drawing showing and example of the construction of a patchantenna that is capable of emitting and receiving circularly polarizedelectric waves.

FIG. 33 is a drawing explaining a first manufacturing method for an RFIDtag.

FIG. 34 is a drawing explaining a second manufacturing method for anRFID tag.

FIG. 35 is a drawing explaining a third manufacturing method for an RFIDtag.

FIG. 36 is a drawing explaining a fourth manufacturing method for anRFID tag.

FIG. 37 is a drawing explaining a fifth manufacturing method for an RFIDtag.

FIG. 38 is a drawing explaining an RFID tag.

FIG. 39 is a drawing explaining the occurrence of problems in a priorRFID tag.

FIG. 40 is a perspective view of a prior RFID tag.

DESCRIPTION OF THE PREFERRED EMBODIMENTS (A) Embodiment 1

FIG. 1 is a drawing explaining the RFID tag of a first embodiment of theinvention, where (A) of FIG. 1 is a pictorial view of the case in whichthe dielectric layer is removed, (B) of FIG. 1 is a side view of inwhich the dielectric layer is transparent, and (C) of FIG. 1 is a topview that shows the positional relationship between the patch antennaand a small dipole antenna. In the side view, in order to make theconstruction easy to understand, the thickness of each part is shownthicker than the actual size.

The RFID tag of this first embodiment is constructed by layering a patchantenna 32 that is formed by printing or etching on an insulating film31 (see (B) of FIG. 1), a small dipole antenna 34 that is formed byetching the surface of a double-sided printed board 33, and ground (GND)35 that is formed by a conductive pattern on the backside of the printedboard 33. A flexible thermoplastic such as polyethylene terephthalate(PET), polyimide (PI), polyethylene naphthalate (PEN), or polyvinylchloride (PVC) can be used as the insulating film 31. A dipole antennahaving a very short length compared to the wavelength λ is called asmall dipole antenna. A dipole antenna is a kind of linear antenna.

In order to make a high-frequency connection between the patch antenna32 and the small dipole antenna 34, a long, narrow slot 36 havingpredetermined dimensions is formed in the patch antenna 32. The smalldipole antenna 34 is straight and has a predetermined line width, andthe LSI chip 37 of the RFID tag is mounted in the center section of thesmall dipole antenna 34 using a chip bonding technique, and conductivepatterns (parallel inductors) 38 a, 38 b for adjusting the impedance areconnected to the left and right of the small dipole antenna 34. Thestraight section on one end of the small dipole antenna 34 is layeredover the slot 36 that is formed in the patch antenna 32 so that itcrosses over the slot, and the small dipole antenna 34 supplies power tothe patch antenna 32 in the high frequency.

The parallel inductors 38 a, 38 b are created in a body with the smalldipole antenna 34, and have predetermined line widths, and the lengthsare adjusted so that the impedance of the tag antenna is matched withthe impedance of the LSI chip 37. FIG. 1 shows an example of connectingtwo parallel inductors 38 a, 38 b, however, it is also possible to useonly one. Also, it is possible to fold the straight section on thebottom side of the dipole antenna 34 to decrease the overall size.

As shown in (A) of FIG. 2, by making the size d of one side of the patchantenna λ/2, and causing the patch antenna to resonate at apredetermined frequency, or in other words, when a current J runs backand forth over the surface of the patch antenna, then as shown in (B) ofFIG. 2, electric wave that is polarized in the Y-axis (horizontal)direction is emitted from the patch antenna in the vertical direction(Z-axis direction). This electric wave is not affected by the materialcharacteristics of the grounded side of the patch antenna. Therefore, inthe case of the RFID tag of this first embodiment, the communicationdistance does not become poor even when the tag is attached to a metalor material including liquid.

Also, the gain of the patch antenna is higher than that of a loopantenna, and by adjusting the thickness, the conductivity of the metal,the dielectric loss or the like, it is possible to increase the gain, soit is possible to make the size of the RFID tag of this first embodimentsmall.

Moreover, with the RFID tag of this first embodiment, it is possible tohigh-frequency connect the small dipole antenna, on which the LSI chipis mounted, to the patch antenna without a DC connection, so there is noneed to form holes in the patch antenna, or to make a DC connection, andthus it is possible to simplify the process of manufacturing the RFIDtag and lower the manufacturing cost.

Furthermore, by connecting loop patterns that function as parallelinductors to the small dipole antenna, and by adjusting the dimensionsof that pattern, or by adjusting the length of the dipole antenna orlength of the slot, it is possible to perform impedance matching betweenthe tag antenna and LSI chip without having to use an impedanceconversion circuit.

(B) Embodiment 2

(a) Construction

A top view of the RFID tag of a second embodiment is shown in (A) ofFIG. 3. In the RFID tag of this second embodiment, a patch antenna 42that functions as the tag antenna, and a small dipole antenna 43 areformed by etching the surface of a double-sided printed board 41, and aconductive pattern (not shown in the figure) on the rear surface of theprinted board is used as ground. A long, thin cutout section 44 isformed in the center of the lower section of the patch antenna 42. Inother words, the cutout section 44 is formed so that it is straight andextends in the direction toward the inside of the patch antenna 42, anda straight section 43 a on one end of the small dipole antenna 43 islocated inside the cutout section 44.

The small dipole antenna 43, which has a predetermined line width,comprises straight sections 43 a, 43 b that are bent into a reversed Lshape, and the LSI chip 45 of the RFID tag is mounted near the bentsection using a chip bonding technique. Also, a conductive pattern(parallel inductor) 46 for adjusting impedance is connected to the rightside of the small dipole antenna 43. The parallel inductor 46 is createdin a body with the small dipole antenna and has a predetermined linewidth, and the length s2 is such that it can be adjusted in order tomatch the impedance of the tag antenna with the LSI chip 37.

The straight section 43 a on one end of the small dipole antenna isinserted into the long, thin cutout section 44 that is formed in thepatch antenna 42, and a high-frequency connection between the smalldipole antenna 43 and patch antenna 42 is realized by way of this cutoutsection. In other words, power is electromagnetically supplied from thesmall dipole antenna 43 to the patch antenna 42 in the high frequency.

The size d of one side of the patch antenna is made to be λ/2, and whenthe patch antenna is made to resonate at a predetermined frequency, orin other words, when a current J is made to run back and forth over thesurface of the patch antenna, similar to as in the case of the firstembodiment, an electric wave is emitted in the vertical direction fromthe patch antenna. This electric wave is not affected by the materialcharacteristics of the grounded side of the patch antenna. Therefore, inthe case of the RFID tag of this second embodiment, the communicationdistance does not become poor even when the tag is attached to a metalor material including liquid.

An example of rectangular cutout sections 47 a, 47 b that are formed onthe end sections of a patch antenna for reducing the size of the boardis shown in (B) of FIG. 3, where the cutouts are formed so that theelectrical length (a1+a2+a3+2×a4) becomes about half the wavelength. Bydoing this, it is possible to shorten the dimension of the vertical sizeby 2×a4. However, when a4 is made too large, the antenna gain decreases,so a proper value must be used.

In this second embodiment shown in (A) and (B) of FIG. 3, both the patchantenna 42 and small dipole antenna 43 were formed on the surface of thesame dielectric body, however, it is also possible for them to belayered; the manufacturing method for each will be described later.Also, the small dipole antenna 43 was bent into a reversed L shape inorder to reduce the size of the board, however, if no importance isplaced on size, the small dipole antenna 43 does not need to be bent.

The actual dimensions and board characteristics of the RFID tag shown inFIG. 3 are shown in (A) and (B) of FIG. 4, where the size of the boardis 78 mm×44 mm×1.2 mm. Also, the line width of one end 43 a of the smalldipole antenna is 2.0 mm, the line width of the other end 43 b is 1.0mm, the space between the cutout 44 and the small dipole antenna 43 is0.5 mm, and the space between the parallel inductor 46 and tip end ofthe patch antenna is 0.5 mm.

Various characteristics have been simulated for the RFID tag of thissecond embodiment that has the dimensions and board characteristicsshown in FIG. 4 as the frequency applied to the patch antenna is changedfrom 850 MHz to 980 MHz. The minimum required power for operating theLSI chip is −10.00 dBm, the power supplied to the reader/writer antennais 27.00 dBm, and the gain thereof is 9.00 dBi.

(b) Characteristics

FIG. 5 shows various simulation results as the frequency was changedfrom 850 MHz to 980 MHz; where: (1) the susceptance Bcp, resistance Rc,reactance Xc of the LSI chip; (2) the resistance Ra, reactance Xa,matching coefficient q, S parameter S11 and gain of the tag antenna; and(3) the communication distance when a linearly polarized wave antennaand a circularly polarized wave antenna are used as the antenna for thereader/writer are shown. The tag antenna is the combination of the patchantenna and small dipole antenna.

Matching Characteristic

FIG. 6 is a Smith chart showing the impedance of the tag antenna, andwhen the frequency changes from 850 MHz to 980 MHz, the impedance of thetag antenna changes as a circle, as shown by the impedance locus IPT.Also, from the characteristics results shown in FIG. 5, the impedance ofthe tag antenna near a frequency of 950 to 953 MHz becomes a value thatis nearly matched with the input impedance of the LSI chip 45.

An equivalent circuit of an RFID tag that comprises an LSI chip and tagantenna is shown in FIG. 7. In other words, the equivalent circuit isexpressed as a parallel circuit of the LSI chip and tag antenna, wherethe LSI chip is represented as a parallel circuit of a resistance Rc andcapacitance Cc (the reactance is Xc), and the tag antenna is representedby a parallel circuit of a resistance Ra and inductance La (thereactance is Xa). The matching conditions in this RFID tag are thatRc=Ra, and |Xc|=Xa, and as can be seen from FIG. 5, at a frequency near950 to 953 MHz, the RFID tag of this second embodiment satisfies thematching conditions.

Gain Characteristic and S11 Characteristic

FIG. 8 shows the gain of the tag antenna as the frequency changes from850 MHz to 980 MHz, and when the patch antenna resonates at a frequencynear 953 MHz, a high gain is obtained.

FIG. 9 shows the S pattern S1 characteristic as the frequency changesfrom 850 MHz to 980 MHz. The S pattern S11 indicates the degree ofimpedance matching with the LSI chip, and has a minimum value at afrequency near 950 to 953 MHz.

Communication Distance

FIG. 10 shows the communication distance as the frequency changes from850 MHz to 980 MHz, and when a linearly polarized wave antenna is usedas the antenna of the reader/writer, the communication distance becomesa maximum at a frequency near 953 MHz. The communication distance r ofthe RFID tag is given by the equation below.

$\begin{matrix}{{r = {\frac{\lambda}{4\;\pi}\sqrt{\frac{{Pt} \cdot {Gt} \cdot {Gr} \cdot q}{Pth}}}}{q = \frac{4\;{{Rc} \cdot {Ra}}}{{{{Zc} + {Za}}}^{2}}}} & 1\end{matrix}$

Here, λ is the wavelength, Pt is the power applied to the reader/writerantenna, Gt and Gr are the respective antenna gains of the tag antennaand reader/writer antenna, and Pth is the minimum value of the powerrequired for the LSI chip to operate. Also, Zc and Za are the compleximpedances of the LSI chip and tag antenna, respectively.

Matching Adjustment

Depending on the dimensions of the parallel inductor 46, there are casesin which impedance matching between the tag antenna and LSI chip is notpossible. In that case, the length s1 of the small dipole antenna or thedimension s2 of the parallel inductor 46 or both s1 and s2 are adjusted.When the dimension s2 is increased, the circle of the impedance locusIPT that is drawn by changing the frequency on the Smith chart shown in(A) of FIG. 11, becomes a little larger moving in the direction of thearrow. This corresponds to the fact that the inductance La of theparallel inductor of the tag antenna in the equivalent circuit shown inFIG. 7 becomes large, and means that it is possible to cancel out aneven larger parallel capacitance Cc of the tag LSI. On the other hand,when the dimension s1 becomes larger, then as shown in (B) of FIG. 11,the impedance locus moves in the direction that the size of the circlebecomes larger without much clockwise or counterclockwise rotation. Thiscorresponds to the fact that the parallel resistance Ra of the tagantenna in the equivalent circuit shown in FIG. 7 becomes small, andmeans that it is possible to cancel out an even smaller parallelresistance of the tag LSI. Therefore, by adjusting the dimension s2 orthe dimension s1 or both dimensions s1 and s2, the impedance locus IPTmoves, and impedance matching can be obtained at a desired frequency.

(c) Effect

With this second embodiment, the emitted electric wave is not affectedby the material on the grounded side of the patch antenna. Therefore,the communication distance does not become poor even when the RFID tagof this second embodiment is attached to a metal or an object includingliquid.

Also, the gain of the patch antenna is higher than that of a loopantenna, and by adjusting the thickness, conductivity of the metal,dielectric loss or the like, it is possible to make the gain evengreater, and thus it is possible to make the size of the RFID tag ofthis second embodiment small.

Moreover, with the RFID tag of this second embodiment the small dipoleantenna on which the LSI chip is mounted and the patch antenna are onlyhigh-frequency connected without being connected by a DC connection, sothere is no need to form holes in the patch antenna, as well as there isno need for a DC connection, making it possible to simplify the processof manufacturing the RFID tag and to reduce the manufacturing cost.

Also, by connecting a loop pattern that functions as a parallel inductorto the small dipole antenna and by adjusting the dimensions of thatpattern, or by adjusting the length s0 of the straight section 43 b ofthe dipole antenna or the length s1 of the cutout section, it ispossible to perform impedance matching with the LSI chip without havingto use an impedance conversion circuit.

(C) Embodiment 3

FIG. 12 is a top view of the RFID tag of a third embodiment of theinvention, where two of the tag antennas of the second embodiment shownin (A) of FIG. 3 are connected in parallel.

Two patch antennas 42, 42′ that function as the tag antenna, and a smalldipole antenna 43 are formed on the top surface of a double-sided printboard 41, and a conductive pattern is formed on the rear surface of theboard (not shown in the figure) as ground. An LSI chip 45 is mounted inthe center of the straight small dipole antenna 43, and the patchantenna 42 and patch antenna 42′ are formed so that they are symmetricalon the left and right with that LSI chip in the center. Also, thepositional relationship between the patch antenna 42 and one end 43 a ofthe small dipole antenna, and the positional relationship between thepatch antenna 42′ and the other end 43 b of the small dipole antenna,are exactly the same. Furthermore, parallel inductors 46 a, 46 b aresymmetrically connected to the upper and lower side of the small dipoleantenna 43.

With the RFID antenna of this third embodiment, it is possible toincrease the gain of the tag antenna, and to transmit electric waves afar distance, however, the size is doubled.

FIG. 13 is a top view of two of the tag antennas of the first embodimentconnected in parallel, and they have the same effect as the RFID tag ofthis third embodiment.

(D) Embodiment 4

(a) Construction

Top views of the RFID tag of a fourth embodiment of the invention areshown in (A) and (B) of FIG. 14, where (A) of FIG. 14 shows the entireRFID tag, and (B) of FIG. 14 is an enlarged view of the section insidethe dashed line. In the RFID tag of this fourth embodiment, a patchantenna 52 that functions as the tag antenna and a small monopoleantenna 53 are etched on the surface of a double-sided print board, anda conductive pattern (not shown in the figure) that is formed on therear surface of the board is used as ground. A monopole antenna having alength that is much shorter than the wavelength λ is referred to here asa small monopole antenna. A monopole antenna is a kind of linearantenna.

A shallow cutout section 52 a is formed on the left side end of thepatch antenna 52, and an antenna section 53 a, having a predeterminedline width, of the small monopole antenna 53 is placed inside the cutoutsection 52 a. A high-frequency connection between the small monopoleantenna 53 and patch antenna 52 is realized by way of the cutout section52 a. In other words, power is supplied in the high frequency from thesmall monopole antenna 53 to the patch antenna 52. In order to make thesize of the board on the right end section of the patch antenna 52small, a cutout section 52 b is formed so that the electrical length(a1+a2+a3+2×a4) is roughly equal to λ/2.

A loop shaped electrically conductive pattern (parallel inductor) 53 bfor adjusting impedance is connected to the tip end of the reversed Lshaped antenna section 53 a of the small monopole antenna 53, and theLSI chip 54 of the RFID tag is mounted in the middle section of the loopusing a chip bonding technique. The parallel inductor 53 b has apredetermined line width and is created in a body with the smallmonopole antenna, and the length s2 is adjusted so that the impedance ofthe tag antenna is matched with the impedance of the LSI chip 54.

By making the length of one side of the patch antenna 52 to be λ/2 andresonating the patch antenna at a predetermined frequency, or in otherwords, by running a current J back and forth over the surface of thepatch antenna, an electric wave is emitted from the patch antenna in thevertical direction as in the case of the first and second embodimentsdescribed above. Therefore, the communication distance does not becomepoor even though the RFID tag of this fourth embodiment is attached to ametal or an object including liquid.

In this fourth embodiment shown in FIG. 14, the patch antenna 52 and thesmall monotone antenna 53 are formed on the same dielectric body,however, it is also possible for them to be layered; the manufacturingmethod for each will be described later.

The actual dimensions and board characteristics of the RFID tag shown inFIG. 14 are shown in (A) and (B) of FIG. 15, where the board size is 78mm×40 mm×1.2 mm. Also, the line width of the small monopole antenna is1.0 mm, and the space between the cutout section 52 a and the smallmonopole antenna 53 is 0.5 mm.

(b) Characteristics

Various characteristics have been simulated for the RFID tag of thisfourth embodiment that has the dimensions and board characteristicsshown in FIG. 15 as the frequency applied to the patch antenna ischanged from 850 MHz to 980 MHz. The minimum required power foroperating the LSI chip is −10.00 dBm, the power supplied to thereader/writer antenna is 27.00 dBm, and the gain is 9.00 dBi.

FIG. 16 shows various simulated results as the frequency was changedfrom 850 MHz to 980 MHz; where: (1) the susceptance Bcp, resistance Rc,reactance Xc of the LSI chip; (2) the resistance Ra, reactance Xa,matching coefficient q, S parameter S11 and gain of the tag antenna; and(3) the communication distance when a linearly polarized wave antennaand a circularly polarized wave antenna are used as the antenna for thereader/writer are shown.

Matching Characteristic

FIG. 17 is a Smith chart showing the impedance of the tag antenna, andas the frequency changes from 850 MHz to 980 MHz, the impedance of thetag antenna changes as a small circle, as shown by the impedance locusIPT. Also, from the characteristics results shown in FIG. 16, theimpedance of the tag antenna near a frequency of 953 MHz becomes a valuethat is nearly matched with the input impedance of the LSI chip 54.

Gain Characteristic and S11 Characteristic

FIG. 18 shows the gain of the tag antenna as the frequency changes from850 MHz to 980 MHz, and when the patch antenna resonates at a frequencynear 953 MHz, a high gain is obtained.

FIG. 19 shows the S pattern S11 characteristic as the frequency changesfrom 850 MHz to 980 MHz. The S pattern S11 indicates the degree ofimpedance matching with the LSI chip, and has a minimum value at afrequency near 953 MHz of −20 dB or less.

Communication Distance

FIG. 20 shows the communication distance as the frequency changes from850 MHz to 980 MHz, and when a linearly polarized wave antenna is usedas the antenna of the reader/writer, the communication distance becomesa maximum at a frequency near 953 MHz.

Matching Adjustment

Depending on the dimensions of the parallel inductor 53 b, there arecases in which impedance matching is not possible. In that case, thedimension s2 of the parallel inductor 53 b is adjusted. When thedimension s2 is decreased, the circle of the impedance locus IPT whichis drawn by changing the frequency on the Smith chart shown in FIG. 21,rotates counterclockwise. Therefore, by adjusting the dimension s2 androtating the circle of the impedance locus IPT, impedance matching canbe obtained at a desired frequency.

(c) Effect

With this fourth embodiment, the emitted electric wave is not affectedby the material on the grounded side of the patch antenna. Therefore,the communication distance does not become poor even when the RFID tagof this fourth embodiment is attached to a metal or an object includingliquid.

Also, the gain of the patch antenna is higher than that of a loopantenna, and by adjusting the thickness, conductivity of the metal,dielectric loss or the like, it is possible to make the gain evengreater, and thus it is possible to make the size of the RFID tag ofthis fourth embodiment small.

Moreover, with the RFID tag of this fourth embodiment the small monopoleantenna on which the LSI chip is mounted and the patch antenna are onlyhigh-frequency connected without being connected by a DC connection, sothere is no need to form holes in the patch antenna, as well as there isno need for a DC connection, making it possible to simplify the processof manufacturing the RFID tag and to reduce the manufacturing cost.

Also, by connecting a loop pattern that functions as a parallel inductorto the small monopole antenna and by adjusting the dimension s2 of thatpattern, or by adjusting the lengths s1 or s3 of the straight section ofthe monopole antenna, it is possible to perform impedance matching withthe LSI chip without having to use an impedance conversion circuit.

(E) Embodiment 5

In the fourth embodiment, a small monopole antenna 53 is placed in theshallow cutout section of the patch antenna 52 as a power supplypattern, and by high-frequency connecting the small monopole antenna 53with the patch antenna 52, power is supplied from the small monopoleantenna 53 to the patch antenna 52. However, construction is alsopossible in which a loop pattern having a predetermined line width isused instead of the small monopole antenna 53, and power is supplied tothe patch antenna from that loop pattern.

(a) Construction

FIG. 22 is a top view of the RFID tag of a fifth embodiment of theinvention. In the RFID tag of this fifth embodiment, a patch antenna 62that functions as the tag antenna, and a loop pattern 63 that functionsas the power supply pattern are formed by etching them on the surface ofa double-sided print board 61, and a conductive pattern (not shown inthe figure) on the rear surface of the board is used as ground.

A shallow cutout section 62 a is formed on the end section on the leftside of the patch antenna 62, and the loop pattern 63, having apredetermined line width, is placed in this cutout section. Ahigh-frequency connection between the loop pattern 63 and patch antenna62 is realized by way of the cutout section, and power is supplied tothe patch antenna 62 from the loop pattern 63 in the high frequency. TheLSI chip 64 of the RFID tag is mounted on the lower end section of theloop pattern using a chip bonding technique. The length s2 (see FIG. 23)of the loop pattern 63 can be adjusted in order to match the impedancebetween the tag antenna and the LSI chip 64. By making the length of oneside of the patch antenna 62 to be λ/2, and causing the patch antenna 62to resonate at a predetermined frequency, or in other words, by runninga current J back and forth over the surface of the patch antenna, anelectric wave is emitted in the vertical direction from the patchantenna as in the case of the first and second embodiments describedabove. This electromagnetic wave is not affected by the materialcharacteristics of the ground side of the patch antenna. Therefore, thecommunication distance does not become poor even though the RFID tag ofthis fifth embodiment is attached to a metal or an object includingliquid.

In the fifth embodiment shown in FIG. 22, the patch antenna 62 and looppattern 63 are formed on the surface of the same dielectric body,however, it is also possible for them to be layered, and themanufacturing method for each will be described later.

The actual dimensions and board characteristics of the RFID tag shown inFIG. 22 are shown in (A) and (B) of FIG. 23. Also, the line width of theloop pattern 63 is 1.0 mm, and the space between the cutout section 62 aand the loop pattern 63 is 0.5 mm.

(b) Characteristics

Various characteristics have been simulated for the RFID tag of thisfifth embodiment that has the dimensions and board characteristics shownin FIG. 23 as the frequency applied to the patch antenna is changed from840 MHz to 980 MHz

Matching Characteristic

FIG. 24 is a Smith chart showing the impedance of the tag antenna, andas the frequency changes from 840 MHz to 980 MHz, the impedance of thetag antenna changes as a small circle, as shown by the impedance locusIPT. Also, the impedance of the tag antenna near a frequency of 953 MHzbecomes a value that is nearly matched with the input impedance of theLSI chip 64.

Gain Characteristic and S11 Characteristic

FIG. 25 shows the gain of the tag antenna as the frequency changes from840 MHz to 980 MHz, and when the patch antenna resonates at a frequencynear 953 MHz, a high gain is obtained.

FIG. 26 shows the S pattern S11 characteristic as the frequency changesfrom 840 MHz to 980 MHz. The S pattern S11 indicates the degree ofimpedance matching with the LSI chip, and has a minimum value at afrequency near 953 MHz of −20 dB or less.

Communication Distance

FIG. 27 shows the communication distance as the frequency changes from840 MHz to 980 MHz, and when a linearly polarized wave antenna is usedas the antenna of the reader/writer, the communication distance becomesa maximum at a frequency near 953 MHz. The communication distance iscalculated presuming that the minimum power required for operation ofthe LSI chip is −10.00 dBm, the parallel resistance Rc of the LSI chipis 800Ω, the parallel capacitance Cc of the LSI chip is 1.2 pF, thereader/writer power is 27.00 dBm, and the gain is 9.00 dBi.

Matching Adjustment

Depending on the dimensions of the loop pattern 63, there are cases inwhich impedance matching is not possible. In that case, the dimension s2of the loop pattern 63 is adjusted. When the dimension s2 is decreased,the circle of the impedance locus IPT that is drawn by changing thefrequency on the Smith chart, rotates counterclockwise (see arrow inFIG. 24). Therefore, by adjusting the dimension s2 and rotating thecircle of the impedance locus IPT, impedance matching can be obtained ata desired frequency.

(c) Effect

With this fifth embodiment, the emitted electric wave is not affected bythe material on the grounded side of the patch antenna. Therefore, thecommunication distance does not become poor even when the RFID tag ofthis fifth embodiment is attached to a metal or an object includingliquid.

Also, the gain of the patch antenna is higher than that of a loopantenna, and by adjusting the thickness, conductivity of the metal,dielectric loss or the like, it is possible to make the gain evengreater, and thus it is possible to make the size of the RFID tag ofthis fifth embodiment small.

Moreover, with the RFID tag of this fifth embodiment the loop pattern onwhich the LSI chip is mounted and the patch antenna are onlyhigh-frequency connected and are not connected by a DC connection, sothere is no need to form holes in the patch antenna, as well as there isno need for a DC connection, making it possible to simplify the processof manufacturing the RFID tag and to reduce the manufacturing cost.

Also, by adjusting the dimension s2 of the loop pattern, or by adjustingthe length s3, it is possible to perform impedance matching with the LSIchip without having to use an impedance conversion circuit.

(F) Sixth Embodiment

This sixth embodiment of the present invention is an embodiment in whichthe size of the RFID tag is made more compact by forming a short circuitbetween one edge of the patch antenna and ground.

(a) Construction

FIG. 28 is a drawing explaining a sixth embodiment of the RFID tag ofthe present invention, where (A) is a pictorial view, (B) is a crosssectional view of section AA in (A), and (C) is a pictorial view as seenfrom the direction of arrow B in (A).

In the fifth embodiment, when the length of one edge of the patchantenna 62 of the RFID tag (FIG. 22) is made to be λ/2 and the antennais caused to resonate at a predetermined frequency, the electric field Ein the Y-axis direction changes as shown in FIG. 29, and the electricfield becomes zero in the center section. This means that it is possibleto emit radio waves in a direction perpendicular to the patch antenna asin the case of the fifth embodiment without the electric fielddistribution changing if the patch antenna and ground are shortcircuited in the center.

The RFID tag of the six embodiment shown in FIG. 28 is short circuitedbetween one edge of the patch antenna 62 and ground 65 on the sidesurface of the substrate 61 by a short-circuit unit 66 based on relatedprinciples, and by doing so, the size of the patch antenna 62 is madeabout ½ the size of that of the RFID tag of the fifth embodiment. Inother words, the length in the Y-axis direction is made to be λ/4.

Other than the point that a short circuit is formed between one side ofthe patch antenna and ground, and the point that the size of the RFIDtag is different, the RFID tag of this sixth embodiment has nearly thesame construction as the RFID tag of the fifth embodiment. The patchantenna 62 that functions as the tag antenna, and the loop pattern 63that functions as the power-supply pattern are both formed on the topsurface of a double-sided printed circuit board 61 by etching, and aconductive pattern 65 ((B) of FIG. 28) on the bottom surface of theprinted circuit board 61 is used as ground, and a short circuit isformed on the side surface of the board between one edge of the patchantenna and ground by a short-circuit unit 66. This short-circuit unit66 can be formed by a plating process.

A cut-out section 62 a is formed on the end section of the patch antenna62, and a loop pattern 63 having a predetermined line width is placed inthe cut-out section. The loop pattern 63 and patch antenna 62 arehigh-frequency connected by way of the cut-out section, and power is inthe high frequency supplied to the patch antenna 62 from the looppattern 63. The LSI chip 64 of the RFID tag is mounted on the endsection of the loop pattern 63 using a chip bonding technique. Thelength s2 of the loop pattern 63 is adjusted so that the impedance ofthe tag antenna is matched with the LSI chip 64. Also, the resonantfrequency can be adjusted by adjusting the depth s5 of a cut-out section67.

Various adjustments are possible using the same methods as those of thefirst through fifth embodiments. For example, by changing the depth s5of the cut-out section 67 formed in the top surface of the patch antenna62, it is possible to adjust the resonant frequency of the patch. Also,by changing the length s2 of the power-supply pattern 63, it is possibleto adjust the input impedance of the tag antenna. As a concrete exampleare the results of simulating the frequency characteristic of theimpedance and the frequency characteristic of the communication distanceshown in FIG. 30 and FIG. 31, respectively.

FIG. 30 shows the impedance locus on a Smith chart when an RFID taghaving a 30 mm×30 mm×2.5 mm dielectric member of which specificdielectric constant is 8.0 and dielectric loss is 0.002, is placed on aninfinite conductive plate. Depending on the dimension s2 of the looppattern 63, it may not be possible to match the impedance, however, inthat case the dimension s2 is adjusted. As the dimension s2 becomessmall, the impedance locus IPT obtained by changing the frequency on theSmith turns in the counterclockwise in the direction of the arrow, so ata desirable frequency, the dimension s2 is adjusted in order to matchthe impedance.

FIG. 31 shows the communication distance when the frequency is changedfrom 900 MHz to 980 MHz. When calculating the communication distance,the characteristic of the tag LSI and reader/writer (RW) antenna aretaken to be as follows. In other words, the impedance of the tag LSI at953 MHz is taken to be 32−j 109[Ω], the power supplied to RW antenna istaken to be 0.5 [W], and the gain of the RW antenna is taken to be9[dBi]. As can be clearly seen from the simulation results of thiscommunication distance, a distance (approximately 2.6 m) in a frequencyband (952-954 MHz) that is practical and sufficient for UHF band RFIDtag can be obtained.

In addition to the advantages of the first to fifth embodiments, thissixth embodiment has the advantage of being able to reduce the size ofthe RFID tag by half.

This sixth embodiment is an embodiment in which the principle of halvingthe size of the tag by forming a short circuit between the patch antennaand ground is applied to the RFID tag of the fifth embodiment, however,the size of the tag can also be halved by applying that principle to theRFID tag of the first to fourth embodiment as well.

(G) Variation

The tag antennas of embodiments 1 to 6 described above, are tag antennasthat emit an electric wave that is linearly polarized in the Y-axisdirection as shown in FIG. 2 in the vertical direction from a horizontalplane (patch antenna surface), and naturally, are capable of receivingan incident electric wave that is linearly polarized in the Y-axisdirection and comes from the vertical direction onto the patch antennasurface. However, these tag antennas are not capable of receiving anelectric wave that is linearly polarized in the X-axis direction.Therefore, the tag antenna is made to be capable of emitting acircularly polarized electromagnetic wave and receiving an incidentelectric wave that is linearly polarized in any direction.

FIG. 32 shows an example of the construction of a patch antenna that iscapable of emitting and receiving a circularly polarized electromagneticwave. An example of cutting part 71, 72 of the patch antenna PATT in adirection that is diagonal to the direction that the current J flowsback and forth is shown in (A) of FIG. 32, and an example forming a slot73 in the patch antenna PATT in a direction that is diagonal to thedirection that the current J flows back and forth is shown in (B) ofFIG. 32.

(H) Manufacturing Method for an RFID Tag

(a) First Manufacturing Method

FIG. 33 is a drawing that explains a first method for manufacturing anRFID tag, and shows an example of applying the method to manufacturingthe RFID tag of the second embodiment; however, the method can also beapplied to manufacturing the RFID tags of the third to fifthembodiments.

A double-sided print board 41 on which an electrically conductivepattern is coated on both sides is prepared, and a patch antenna 42 thatfunctions as the tag antenna, a small dipole antenna 43 on which an LSIchip is to be mounted, and a parallel inductor 46 are formed by etchingthe surface of that double-sided print board 41. Next, an LSI chip 45 ismounted on the small dipole antenna 43 by chip bonding, to create theRFID tag. The conductive pattern on the rear surface of the double-sidedprint board 41 is used as the ground GND of the tag antenna.

(b) Second Manufacturing Method

FIG. 34 is a drawing that explains a second method for manufacturing anRFID tag, and shows an example of applying the method to manufacturingthe RFID tag of the second embodiment; however, the method can also beapplied to manufacturing the RFID tags of the third to fifthembodiments.

A patch antenna 42 that functions as the tag antenna, a small dipoleantenna 43 on which an LSI chip is to be mounted, and a parallelinductor 46 are formed by printing or etching an insulating film 41 asuch as PET, and an LSI chip 45 is mounted on the small dipole antenna43 by chip bonding.

Next, a single-sided print board 41 b on which an electricallyconductive pattern is coated on one side is prepared, and the insulatingfilm 41 a is attached to the surface of the single-sided print board 41b on which the conductive pattern is not formed using adhesive,double-sided tape or the like, to create the RFID tag.

The conductive pattern on the rear surface of the single-sided printboard 41 b is used as the ground GND of the tag antenna. Also, byforming a depression 48 on the single-sided print board 41 b, andplacing the LSI chip in that depression 48, the insulating film 41 awill not be uneven.

(c) Third Manufacturing Method

FIG. 35 is a drawing that explains a third method for manufacturing anRFID tag, and shows an example of applying the method to manufacturingthe RFID tag of the second embodiment; however, the method can also beapplied to manufacturing the RFID tags of the third to fifthembodiments.

A patch antenna 42 that functions as the tag antenna, a small dipoleantenna 43 on which an LSI chip is to be mounted, and a parallelinductor 46 are formed by printing or etching an insulating film 41 asuch as PET, and an LSI chip 45 is mounted on the small dipole antenna43 by chip bonding.

Next, a dielectric body 41 c such as PET, and an electrically conductivesheet 41 d such as copper or aluminum are prepared, and the insulatingfilm 41 a is attached to one surface of the dielectric body 41 c usingadhesive, double-sided tape or the like, and the conductive sheet 41 dis attached to the other side of the dielectric body 41 c to create theRFID tag.

By forming a depression 48 on the dielectric body 41 c, and placing theLSI chip in that depression 48, the insulating film 41 a will not beuneven.

(d) Fourth Manufacturing Method

FIG. 36 is a drawing that explains a fourth method for manufacturing anRFID tag, and shows an example of applying the method to manufacturingthe RFID tag of the second embodiment; however, the method can also beapplied to manufacturing the RFID tags of the first and third to fifthembodiments.

A small dipole antenna 43 on which an LSI chip is to be mounted, and aparallel inductor 46 are formed by printing or etching an insulatingfilm 41 a such as PET, and an LSI chip 45 is mounted on the small dipoleantenna 43 by chip bonding.

Also, a double-sided print board 41 e that is coated with anelectrically conductive pattern on both sides is prepared, and a patchantenna 42 that functions as the tag antenna is formed on the surface ofthe double-sided print board 41 e by etching, and the conductive patternon the rear side of the double-sided print board 41 e is used as theground GND of the tag antenna.

Next, the insulating film 41 a is attached to the surface of thedouble-sided print board 41 e on which the patch antenna 42 is formedusing adhesive, double-sided tape or the like, to create the RFID tag.

By forming a depression 48 on the double-sided print board 41 e, andplacing the LSI chip in that depression 48, the insulating film 41 awill not be uneven.

With this fourth manufacturing method, it is possible to use in commonan insulating film 41 a in all countries, even if the frequency bandthat is used differs according to country. That is, it is sufficient foreach country to prepare a patch antenna which resonates by a frequencyused in the country.

(e) Fifth Manufacturing Method

FIG. 37 is a drawing that explains a fifth method for manufacturing anRFID tag, and shows an example of applying the method to manufacturingthe RFID tag of the second embodiment; however, the method can also beapplied to manufacturing the RFID tags of the first and, third to fifthembodiments.

A patch antenna 42 that functions as a tag antenna is formed on aninsulating film 41 a such as PET by printing or etching.

Also, a double-sided print board that is coated with an electricallyconductive pattern on both sides is prepared, and a small dipole antenna43 on which an LSI chip will be mounted and a parallel inductor 46 areformed on the surface of the double-sided print board 41 e by etching,and then an LSI chip 45 is mounted on the small dipole antenna 43 bychip bonding.

The conductive pattern on the rear side of the double-sided print board41 e is used as the ground GND of the tag antenna.

Next, the insulating film 41 a is attached to the surface of thedouble-sided print board 41 e on which the small dipole antenna 43 isformed using adhesive, double-sided tape or the like, to create the RFIDtag.

With this fifth manufacturing method, it is possible to use in common adouble-sided print board 41 e in all countries, even if the frequencyband that is used differs according to country. That is, it issufficient for each country to prepare an insulating film 41 e on whicha patch antenna is formed.

As many apparently widely different embodiments of the present inventioncan be made without departing from the spirit and scope thereof, it isto be understood that the invention is not limited to the specificembodiments thereof except as defined in the appended claims.

1. A tag having a patch antenna that functions as the tag antenna, comprising: a small dipole antenna having two straight sections connected at a bent section, one end of the straight sections being located inside a cutout section of the patch antenna, the cutout section being straight and extending from the center of an edge toward the inside of the patch antenna; a loop pattern connected to the small dipole antenna and functioning as a parallel inductor; and an LSI chip mounted to the small dipole antenna near the bent section; wherein in operation, a high-frequency connection between the small dipole antenna and the patch antenna is realized by way of the cutout section, by which high-frequency connection power is electromagnetically supplied from the small dipole antenna to the patch antenna.
 2. The RFID tag of claim 1 further comprising: a dielectric member having said small dipole antenna, said loop pattern, said LSI chip and said patch antenna formed on one side, and a conductive pattern that functions as a ground formed on the other side. 